Team admins who have not enabled early access to improved team folders can create a new team folder, rather than renaming an existing one. Team admins can then transfer the contents from the old team folder to the new one:

Only the owner of a shared folder can move it out of the team folder. If you're not the owner of a shared folder, contact the owner to remove it from the team folder. You can also contact your team admin.

I'm trying to move a shared folder into a team folder

Only the owner of a shared folder can move it into a team folder. If you're not the owner of a shared folder, you cannot move it to a team folder. However, you can contact the shared folder owner and request that they do this for you.